In high performance liquid chromatography, a liquid has to be provided usually at a very controlled flow rate and at high pressure at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase, thus separating different compounds of the sample fluid which may then be identified.
The mobile phase, for example a solvent, is pumped under high pressure typically through a column of packing medium, and the sample to be analyzed is injected into the column. As the sample passes through the column with the liquid, the different compounds, each one having a different affinity for the packing medium, move through the column at different speeds. Those compounds having greater affinity for the packing medium move more slowly through the column than those having less affinity, and this speed differential results in the compounds being separated from one another as they pass through the column.
The mobile phase with the separated compounds exits the column and passes through a detector, which identifies the molecules, for example by spectrophotometric absorbance measurements. A two-dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made, and from the chromatogram the compounds may be identified. For each compound, the chromatogram displays a separate curve or “peak”. Effective separation of the compounds by the column is advantageous because it provides for measurements yielding well defined peaks having sharp maxima inflection points and narrow base widths, allowing excellent resolution and reliable identification of the mixture constituents. Broad peaks, caused by poor column performance, so called “Internal Band Broadening” or poor system performance, so called “External Band Broadening” are undesirable as they may allow minor components of the mixture to be masked by major components and go unidentified.
An HPLC column typically comprises a stainless steel tube having a bore containing a packing medium comprising, for example, silane derivatized silica spheres having a diameter between 0.5 to 50 μm, or 1-10 μm or even 1-7 μm. The medium is packed under pressure in highly uniform layers which ensure a uniform flow of the transport liquid and the sample through the column to promote effective separation of the sample constituents. The packing medium is contained within the bore by porous plugs, known as “frits”, positioned at opposite ends of the tube. The porous frits allow the transport liquid and the chemical sample to pass while retaining the packing medium within the bore. After being filled, the column may be coupled or connected to other elements by e.g. using fitting elements. Such fitting elements may contain porous parts such as screens or frit elements.
During operation, a flow of the mobile phase traverses the column filled with the stationary phase, and due to the physical interaction between the mobile and the stationary phase a separation of different compounds or components may be achieved. In case the mobile phase contains the sample fluid, the separation characteristics is usually adapted in order to separate compounds of such sample fluid. The term compound, as used herein, shall cover compounds which might comprise one or more different components. The stationary phase is subject to a mechanical force generated in particular by a hydraulic pump that pumps the mobile phase usually from an upstream connection of the column to a downstream connection of the column. As a result of flow, depending on the physical properties of the stationary phase and the mobile phase, a relatively high pressure occurs across the column.
Fittings for coupling different components, such as separation columns and conduits, of fluidic devices are commercially available and are offered, for instance, by the company Swagelok. A typical tube fitting is disclosed in U.S. Pat. No. 5,074,599 A.
WO 2010/000324 A1, by the same applicant, discloses a fitting for coupling a fluid conduit to another component of a fluidic device.
U.S. Pat. No. 6,827,095 B2 discloses modular microfluidic systems with planar couplers coupled between. Planar couples from micro-machined titanium for high pressure microfluidic applications are disclosed by the same applicant in US 2008/0142479 A1.
WO 2009/121410 A1, by the same applicant, discloses planar fluidic conduits and the coupling thereof to other devices.